1. Field of the Invention
The present invention relates to a lubricating oil additive composition which provides excellent oxidation stability, low susceptibility to carbonization and high cleanability. The invention further relates to a process for preparing a lubricating oil additive composition, and a lubricating oil containing the additive.
2. Description of the Background Art
Engine oils are generally mixed with additives for dispersing sludge and the like in order to keep the interior of the engine clean and to neutralize acidic substances produced during the combustion of fuel. Such additives generally prevent corrosive wear.
Salicylates have heretofore been prepared by alkylating phenol with an alpha-olefin, converting the resulting alkylphenol into an alkali metal salt thereof, reacting carbon dioxide with the alkali metal salt to provide an alkali metal salt of alkylsalicylic acid, decomposing the resultant salt with a mineral acid such as sulfuric acid to remove the alkali metal or metathesizing the salt with the chloride of a divalent metal and then adding the oxide and/or the hydroxide of a divalent metal to react with carbon dioxide.
However, this process involves a significant drawback in that the alkali metal used in the reaction can not be completely removed. Consequently, the performance of the salicylate as an oil additive is deteriorated because the alkali metal salt of the alkylsalicylic acid is oil-soluble and hence fails to come into sufficient contact with the mineral acid or the chloride of the divalent metal, which is water-soluble. Further, water containing alkali metal salts can not be fully removed from the reaction product.
On the other hand, Japanese patent application Laid-Open No. 127396/1985 discloses a process for the preparation of a salicylate which does not use alkali metal in which an alkaline earth metal is added to phenol, and the addition product is treated with carbon dioxide. However, this process involves significant drawbacks in that a major amount of phenol remains unreacted due to its low rate of reaction, and phenol removal by distillation is difficult, particularly in an industrial setting.